To install a window in a sloped roof, one at first needs to mount a window frame in the roof by means of supporters, then fit a glazed sash in the frame, and equip the frame and the sash with a covering and a flashing member as well as some other necessary parts.
Such a window satisfies people's normal use in a sloped roof.
Typically, a sloped roof window comprises a window frame, a sash frame, coverings, flashing members, and sealing elements. The top, bottom and lateral frame members of the window frame and the sash frame need coverings for covering the frames and protecting the wood or other material of the window from the weather such as rain, sunshine and blizzard. Meanwhile, there is a sealing provided between the frame and the sash.
The conventional window frame and sash is made of wood, in order to provide a sealing for the window, and to protect the wooden material, people usually use sealing pads or strips. Since wood tends to swell and deform due to exposure thereof to rain and moisture, people mainly consider protection of the wooden members at the outer surface of the frame and the sash, in order to isolate the wooden members from rain and moisture.
However, the window is frequently opened for ventilation, inevitably the weather will affect the wood, besides other surrounding factors. In particular when raindrops adhere the inner side of the window frame or the outer side of the sash exposed to the surroundings, the raindrops drip down along the inner surface of the window frame and the outer surface of the sash. Therefore, the seal will fail finally no matter what a good new one it is. In other word, as the time goes on, the sealing effect will go worse and the wooden members will be eroded. Besides, the temperature difference between the indoor and the outdoor causes the moisture at the inner surface of the window glass condense to water, which erodes the wooden window.
What's more, no matter which the reason for the erosion of the window wood is, rain, moisture or condensate, they all can adhere themselves on the wooden window for a long time, for example on the inner surface and the outer surface of the sash, or they can stay in cavities formed between the frame and the sash. As the cumulated water cannot be discharged soon, the penetration of the rain or water into the wood cannot be stopped in time. This is another considerable reason for erosion of the wooden window.
To solve the above disadvantages, people have tried hard to improve the structure of the window. As disclosed in WO99/51831 “A ROOF WINDOW WITH MAIN FRAME AND SASH COVERING MEMBERS”, the bottom frame member of the window frame is covered by an covering, while the bottom member of the sash frame is covered by another covering, which covers the covering for the bottom member of the window frame. The cavity formed between coverings can generate vertexes, which prevent the window frame and the sash frame from the weather. Although the coverings are well windproof and waterproof, it is possible that rain, dew and condensate still enter into the window.
Materials for manufacturing windows have changed. Aluminum alloy, plastic, metal and nonmetal complex are used for making windows. Some high strength, waterproof and erosion-resistant materials are used for manufacturing the window frame and the sash frame. Now, people are trying to solve the sealing problem in roof windows.